Using Call Flows to Resolve Call Processing Problems

This topic provides information about a typical call flow in an IP telephony environment. Figure 1 shows a call flow that illustrates the actions in a typical call between the following devices at two different sites:

•Cisco Unified IP Phone (SCCP)

•Cisco Unified Communications Manager

•Gatekeeper

Figure 1 Call Flow in an IP Telephony Environment

Figure 2 Call Flow in an IP Telephony Environment (continued)

Figure 3 Call Flow in an IP Telephony Environment (continued)

Figure 4 Call Flow in an IP Telephony Environment (continued)

Figure 5 Call Flow in an IP Telephony Environment (continued)

For both successful and unsuccessful calls, an industry-standard cause code value appears in the disconnect or release signaling messages. The cause code reveals if the call was disconnected normally (typically cause code 16) or abnormally. Table 1 lists the standard cause values that may appear in the trace files as part of disconnect processing.

Table 1 Disconnect Cause Code Values

Hexadecimal Code with High-Order Bit Set

Hexadecimal Code Without High-Order Bit Set

Decimal Code

Description

0x81

0x01

1

Unallocated (unassigned) number. This cause indicates that the destination requested by the calling user cannot be reached because the number is unassigned. This number is not in the routing table, or it has no path across the ISDN network.

0x82

0x02

2

No route to specified transit network (National use). This number was dialed with a transit network code such as 108880 to go from AT&T and MCI, and there is no route across. The wrong transit network code was dialed.

0x83

0x03

3

No route to the destination. The dialed number is in the routing plan, but there is no physical route to the destination. The most likely cause of this is that the PRI D-channel is down, or the span or WAN is not connected correctly.

0x84

0x04

4

Send special information tone.

0x85

0x05

5

Misdialed trunk prefix (National use).

0x86

0x06

6

Channel unacceptable.

0x87

0x07

7

Call awarded and being delivered in an established channel.

0x88

0x08

8

Preemption.

0x89

0x09

9

Preemption. Circuit reserved for reuse.

0x90

0x10

16

Normal call clearing. This is one of the most common codes and is received for many reasons. It usually occurs because someone hung up the call.

0x91

0x11

17

User busy. The number dialed is busy and cannot receive any more calls.

0x92

0x12

18

No user responding. The number that is being dialed has an active D-channel, but the far end chooses not to answer.

0x93

0x13

19

No answer from the user (user alerted). The number that is being dialed has an active D-channel, but the far end chooses not to answer.

0x94

0x14

20

Subscriber absent.

0x95

0x15

21

Call rejected.

0x96

0x16

22

Number changed. This cause code is generated when a subscriber on the PSTN has changed his or her phone number. Usually this message is accompanied by a progress indicator stating that in-band information is available. The PSTN provides an announcement in-band indicating the new phone number, if available.

0x9A

0x1A

26

Nonselected user clearing.

0x9B

0x1B

27

Destination is out of order. The number dialed is a working number, but the span is not active.

0x9C

0x1C

28

Invalid number format (address incomplete). This can happen when you are calling out using a network type number (enterprise) when you should be calling out Unknown or National.

0x9D

0x1D

29

Facility rejected.

0x9E

0x1E

30

Response to STATUS ENQUIRY.

0x9F

0x1F

31

Normal, unspecified. This is another common code. It happens when the network cannot determine what to do with the call being made.

0xA2

0x22

34

No circuit/channel is available. No B-channels are available to make the selected call.

0xA6

0x26

38

Network is out of order.

0xA7

0x27

39

Permanent frame mode connection is out of service.

0xA8

0x28

40

Permanent frame mode connection is operational.

0xA9

0x29

41

Temporary failure. The call was disconnected due to a network failure. This code appears for some long distance providers if the hunt sequence is incorrect. PRI lines must be set up for a flex hunt sequence (not a float hunt sequence).

0xAA

0x2A

42

Switching equipment congestion.

0xAB

0x2B

43

Access information discarded. Usually reported when the far-end ISDN switch removes some piece of information before tandem-switching a call. For example, some PBXs strip the display IE before sending a call out toward the PSTN and send back a message with this cause code.

0xAC

0x2C

44

Requested circuit/channel is unavailable. This happens when you get in a glare condition: Both sides are selected top-down or bottom-up. Change the Allocation Direction (so that one end is top-down and the other is bottom-up).

0xAE

0x2E

46

Precedence call blocked.

0xAF

0x2F

47

Resource unavailable, unspecified. Whenever you see Cisco Unified Communications Manager initiate a disconnect with cause code 0xAF, 99% of the time the problem is related to a media setup failure. Check for codec capabilities mismatches, especially your regions configuration.

0xB1

0x31

49

Quality of service unavailable.

0xB2

0x32

50

Requested facility not subscribed. This code typically indicates you are trying to use a service you are not permitted to use. For example, you might be trying to make a voice call on an ISDN circuit provisioned for data only.

0xB5

0x35

53

Outgoing calls barred within Closed User Group (CUG).

0xB7

0x37

55

Incoming calls barred within CUG.

0xB9

0x39

57

Bearer capability not authorized. This code indicates that you are placing a call with a bearer capability you are not allowed to use.

0xBA

0x3A

58

Bearer capability not presently available. This code indicates that you are placing a call with a bearer capability for which the service provider does not currently have capacity to supply.

Bearer capability not implemented. The cause could be one of the following occurrences:

•You need to change the PCM Type value to the setting appropriate for your country. This is the most common cause, especially in countries where G.711 A-law companding is the standard. If your gateway is configured for Âµ-law and the service provider or PBX is expecting A-law, you will see calls disconnected with this cause code.

•The central office (CO) does not understand an information element in the setup message.

•You are connected to a PBX and you are sending out a network type number when the switch accepts only Unknown or National.

•You are selecting European PRI and you have the progress indicators turned on when they should be off.

0xC2

0x42

66

Channel type not implemented.

0xC5

0x45

69

Requested facility not implemented.

0xC6

0x46

70

Only restricted digital information bearer capability is available (National use).

0xCF

0x47

79

Service or option not implemented, unspecified.

0xD1

0x51

81

Invalid call reference value. This code indicates that the far-end switch did not recognize the call reference for a message sent by the gateway.

0xD2

0x52

82

Identified channel does not exist. This code indicates a call attempt on a channel that is not configured on the far end. This could happen if you are using a fractional PRI. As of Cisco Unified Communications Manager Release 3.3, fractional PRIs are no longer supported.

0xD3

0x53

83

A suspended call exists, but this call identity does not.

0xD4

0x54

84

Call identity in use.

0xD5

0x55

85

No call suspended.

0xD6

0x56

86

Call having the requested call identity has been cleared.

0xD7

0x57

87

User is not a member of CUG.

0xD8

0x58

88

Incompatible destination. The cause could be one of the following occurrences:

•The number being dialed is not capable of the type of call.

•You are calling a restricted line in unrestricted mode.

•You are calling a POTS phone using unrestricted mode.

0xDA

0x5A

90

Nonexistent CUG.

0xDB

0x5B

91

Invalid transit network selection (National use).

0xDF

0x5F

95

Invalid message, unspecified.

0xE0

0x60

96

Mandatory information element is missing. The far-end switch states that a message was received missing an information element it considers to be mandatory per the Q.931 specification.

0xE1

0x61

97

Message type nonexistent or not implemented.

0xE2

0x62

98

Message is incompatible with the call state, or the message type is nonexistent or not implemented. This code is usually indicative of an ISDN protocol mismatch. Each ISDN protocol variant has a slightly different state machine based on the state machines defined in the Q.931 specification. If the two sides of an ISDN connection are not configured for the same protocol, one side might violate the other's call state machine. If an ISDN message is sent that is not expected in the current call state, this cause is generated.

0xE3

0x63

99

An information element or parameter does not exist or is not implemented.

0xE4

0x64

100

Invalid information element contents. The cause could be one of the following occurrences:

•The call has an information element that is not understood by the switch being called. The E4 is usually followed by the information element that is causing the problem.

•The most common problem is that you are trying to place a call using a network number when the switch being called accepts only National, International, or Unknown dialing.

•This code is also generated when you are using Network-Specific Facilities as an element when they are not needed.

0xE5

0x65

101

The message is incompatible with the call state. This code is usually indicative of an ISDN protocol mismatch. Each ISDN protocol variant has a slightly different state machine based on the state machines defined in the Q.931 specification. If the two sides of an ISDN connection are not configured for the same protocol, one side might violate the other's call state machine. If an ISDN message is sent that is not expected in the current call state, this cause is generated.

0xE6

0x66

102

Recovery on timer expiry. This occurs when ISDN messages don't arrive in specified time according to the Q.931 specification. The E6 is sometimes followed by the timer that has expired (for example, 03 01 00—the 310 timer).